RFID technology employs a radio frequency (RF) wireless communication link and small embedded integrated circuitry-based labels or electronic transponders (“tags”) to create a system allowing physical objects to be uniquely identified and their movements tracked. The tags function as item-level unique “RF barcodes” that communicate with a reader device (also referred to as an “interrogator” or “reader”) without requiring line-of-sight scanning or singulation of the objects. The action of “reading” a tag refers to an RFID reader-device electronics transmitting interrogation messages to the proximately disposed tag or tags and receiving response signal(s) in return.
The embedded tags are generally “passive,” meaning they have no batteries but are instead powered entirely by the RF interrogation field of the reader device. Many of the features of today's passive tags have been described by one of the present inventors in U.S. Pat. Nos. 5,523,749 and 5,793,305, which are hereby incorporated by reference in their entirety.
A typical RFID system includes two primary types of components: a reader device and a tag. The tag is typically a miniature label-like device assembly containing an integrated circuit (“IC”) chip and an antenna mounted on a flexible plastic or paper substrate, capable of responding, via a wireless air interface channel, to an RF interrogation signal generated and transmitted by the reader device. The tag is configured to generate a return reply signal in response to the RF interrogation signal emitted by the reader, the response signal being modulated in a manner to convey identification or other data stored within the tag or remotely in the cloud (e.g., on the Internet) back to the reader device. As used herein, the term “cloud” is meant to broadly encompass all remote data storage configurations. There are many different types of RFID systems, used in numerous different and varied applications, implementing different air interface and data communication protocols.
Some applications may require an RFID reader to interrogate (read) multiple tags (attached to different products) in a single interrogation session. This may happen, for example, in inventory applications, where a reader is located some distance away from multiple products with tags on them, and the interrogation signal generated and broadcasted by the reader reaches multiple tags at substantially the same time. In such multi-tag reading environments, because different tags may respond to the same interrogation signal at the same time, their return reply signals may collide (interfere with each other), preventing the reader from successfully reading the tags. To overcome this type of problem in multi-tag reading environments, some RFID systems use what are called anti-collision communication protocols. Such protocols either minimize the chances of collisions occurring or can recover from the detected collisions, allowing the reader to successfully read the entire population of tags.
In applications where a reader is very close to a tag, essentially creating a single-tag reading environment, the danger of collisions or signal interferences is very low. As a result, communication protocols utilized in such application either do not have anti-collision features or have very weak anti-collision features. One example of such a protocol is a Near Field Communication (“NFC”) protocol, in which a reader is generally positioned less than a few centimeters away from a tag.
In the NFC protocol, however, tag-to-reader communications take place in response to commands issued and transmitted to a tag by the reader. Such communication protocols are referred to as “command-and-control” protocols.
In contrast, some protocols do not require the reader to send out commands. Instead, once an interrogation signal has powered up a tag and the protocol has been detected by the tag's circuitry, the tag returns a reply signal without waiting for any interrogator commands. Such protocols are referred to as “commandless” protocols.
RFID systems can generally be separated into three frequency-dependent categories—(1) systems operating in a low frequency (“LF”) band (from 125 kHz to 134 kHz), (2) systems operating in a high frequency (“HF”) band (from 3 MHz to 30 MHz), and (3) systems operating in an ultrahigh frequency (“UHF”) band (from 860 MHz-960 MHz)—each category having its own characteristics and presenting different technological challenges for RFID system designers. Presently, however, most of the technical discipline and use cases of RFID technology lay in the HF and UHF categories, each imposing different design constraints. For example, tags operating in the HF frequency band typically require a multi-turn loop style magnetic H-field responsive antenna, while tags operating in the UHF band typically use an electric E-field responsive dipole-style antenna.
Another distinguishing feature between HF and UHF RFID systems is the way energy transfer between reader and the passive tag is conducted. For example, in RFID systems operating in the HF band, energy transfer occurs entirely through inductive coupling by RF transformer action, by means of the magnetic H-field and associated magnetic flux lines passing through the proximate tag antenna coil [loop]. As a result, energy coupling for both transponder powering and data exchange occurs via the highly localized near-field, where radio frequency signals decay very rapidly over a relatively short distance. Because of the inherent near-field characteristic of the H-field technology, the interrogation and tag response signals of HF systems die off very rapidly beyond the intended coverage area. Consequently, surrounding environmental effects and variations have much less of an impact on HF-system performance, resulting in very robust tag reading characteristics.
On the other hand, RFID systems operating in the UHF band work by the energy transfer and data communication mechanism of far-field radio propagation of an electromagnetic wave that is radiated from an RFID reader antenna and propagates great distances in free space, imparting long-range capability to such RFID systems. Real power measured in units of Watts/m2 is conveyed in the propagating wave by an E×H Poynting vector and the notion of adjusting the radiated reader power to establish and define an arbitrary read-zone size. The tag data reply communication is produced by reflection of a small amount of that incident RF power in the form of modulated backscattered radio waves to convey communication protocol control signals and identification information from the tag to the distant reader. Unlike the HF systems, UHF systems suffer from environmental multipath propagation problems.
Increasing the radiated power emanating from the UHF reader antenna increasingly illuminates a larger 3-dimensional volume of space containing a broad constellation of tags placed on a variety of different physical objects. The greater the antenna radiated power, the greater the attainable powering and communication distance between the reader and tags.
In such radiated UHF electromagnetic wave, the propagated energy disperses and dissipates at a relatively slow rate with a gentle 1/R2 decay law (where R is a distance from the reader's antenna to the tag). As a result, the more uniformly spread UHF reader energy can power and communicate with passive RFID tags over distances spanning many meters. Because the extent and coverage of the attainable read zones is proportional to the RF power level, higher radiated power directly equates to larger read zone, with a substantial increase in the tag's effective powering and communication distances.
By contrast, in an inherently shorter-range magnetic field (“H-field”) inductively coupled HF RFID system, tag powering and tag-to-reader communication is considered to be a coupled RF (“RF transformer”) configuration, in which the primary winding of the notional transformer comprises the reader antenna coupler coil and the secondary winding of the notional transformer comprises the tag's coil. Any impedance change in the secondary winding of the “air coupled” RF transformer caused by tag load modulation of the magnetic flux line linkages is transformed into a small information and data carrying back-EMF in the reader antenna coupler coil, in which the small-signal perturbations are duly sensed and decoded by RF receiver circuitry in the reader.
Driving an RF current through the reader's antenna coupler coil creates a highly localized magnetic field, the intensity of which in units of amperes/meter (A/m) is directly proportional to the current. The magnetic flux associated with that local field integrates the field over a local surface area and is the appropriate metric in considering the total amount of magnetic field passing through the proximate tag coil. The resultant energizing voltage induced in the tag coil is proportional to (i) the number of magnetic flux lines passing through the enclosed area and (ii) number of loop turns comprising the tag coil. This is classical transformer action between two proximate coils having mutual inductance and an associated coupling coefficient.
One important characteristic of such magnetic-energy-exchange configurations lies in the spatial extent of the three-dimensional field coverage provided by the reader. In these configurations, the three-dimensional field coverage is primarily determined by the geometry and dimensional size of the reader's antenna coupler coil. Within the physically enclosed coil boundaries, the magnetic field and flux in the lateral direction are reasonably constant in magnitude. Beyond those enclosed coil area boundaries, however, magnitude of the field rapidly decays with distance R from the antenna following a very steep inverse cube 1/R3 relationship. As a result, incrementally changing magnetic field strength at the reader's antenna by increasing the antenna coil RF current does not change and extend interrogation distance coverage in any appreciable manner. Instead, the interrogation distance coverage depends primarily on the magnitude of the tag's activation field-strength threshold.
Another distinguishing feature of the HF magnetic fields is their tolerance and immunity to the deleterious effects of liquids and lossy dielectric materials associated with many items to which the tags are attached. These robust environmental tolerance characteristics contrast with UHF RFID systems, which exhibit constrained read performance in this respect.
Accordingly, as explained above, important operational distinctions exist between radiative far-field UHF RFID systems and the inductive near-field magnetic H-field coupled HF RFID systems. Within the HF system category of RFID, however, there exists a further technology subdivision of very-short-range NFC identification systems, earlier identified. This subdivision is predominantly based around the now ubiquitous smartphone as the consumer empowered electronic label reading device that can read tags at up to only a few centimeters. These systems use a well-known NFC communication protocol that operates at a single 13.56 MHz carrier frequency, which is in the HF band. Notably, today's smartphones and other RFID-enabled consumer devices do not embrace UHF readers for UHF tags.
It is known to have a multi-frequency passive tag with two operational modes, one mode using a communication protocol in the HF band, e.g., the very-short-range NFC protocol, and the other mode using a second communication protocol in the UHF band. Because of the fundamental differences in the requirements of the HF and UHF systems, however, including the use of very different carrier frequencies, such prior art tag utilizes dual antennas and an application specific integrated circuit (“ASIC”) that is complex, making both the ASIC and overall tag large and expensive. As a result, such a tag is not useful for ultra-low-cost applications and where hundreds of billions, even trillions of items globally need to be uniquely identified.
Despite the different RFID system architectures and protocols that exist today, there is need for a passive low cost tag having a dual personality with two distinct modes of air interface protocol operation, wherein one mode the tag is capable of being read by an interrogator using one communication protocol, and alternatively by another interrogator operating in the same zone (geographical/jurisdictional area or location) by means of a different protocol, such that both protocols operate on substantially the same carrier frequency.
Furthermore, there is need for a passive low cost tag that has a dual personality with two distinct modes of air interface protocol operation, wherein one mode the tag is capable of being read by an interrogator at close proximity range and alternatively by another interrogator operating in the same zone (geographical/jurisdictional area or location) by means of a different multi-tag reading protocol capable of reading a tag at a non-close (long) ranges utilize substantially the same carrier frequency.
Furthermore, there is need for a passive low cost tag that having a dual personality with two distinct modes of air interface protocol operation, wherein one mode the tag is capable of being read by an interrogator at close proximity range by a command-and-control type protocol and alternatively by another interrogator operating in the same zone (geographical/jurisdictional area or location) by means of a different multi-tag reading protocol having robust anti-collision features and capable of reading a tag at a non-close (long) range, such that both protocols utilize substantially the same carrier frequency.
Furthermore, there is need for a passive low cost tag that has a dual personality with two distinct modes of air interface protocol operation, wherein one mode the tag is capable of being read by an interrogator at close proximity range by a command-and-control type protocol and alternatively by another interrogator operating in the same zone (geographical/jurisdictional area or location) by means of a commandless multi-tag reading protocol having robust anti-collision features and capable of reading a tag at a non-close (long) range, such that both protocols utilize substantially the same carrier frequency.
Furthermore, there is need for a passive low cost tag that has a dual personality with two distinct modes of air interface protocol operation, wherein one mode the tag is capable of being read by an interrogator at close proximity range by an NFC-type protocol and alternatively by another interrogator operating in the same zone (geographical/jurisdictional area or location) by means of a commandless multi-tag reading protocol having robust anti-collision features and capable of reading a tag at a non-close (long) range, such that both protocols utilize substantially the same carrier frequency, such as 13.56 MHz.
Furthermore, there is need for a dual-mode, low cost, passive tag using a single multi-turn loop antenna to communicate with different interrogators that utilize different communication protocols operating on substantially the same carrier frequency.
Furthermore, there is need for an RFID system that utilizes the invented dual-mode passive tag, wherein interrogator-to-tag reading range is increased using an improved interrogator circuitry comprising a directional interrogator antenna with an axially focused magnetic field.
The RFID industry is full of inefficient compound margins, fragmented solutions, and cost and value propositions that are out of synch. It is an object of the present invention to fill a long felt need and perceived failure of others to address problems facing particular technical and market areas that have gone unsolved for a long time and to overcome deficiencies of the prior art.
Improved functionality and lower-cost RFID tag technology of the present dual personality invention will support ALL brands and retailers irrespective of size, enabling customer retention—both online and offline—as well as facilitating direct two-way consumer interactions and user experiences, enabling product authentication, willingly received personalized [pull] advertising, manuals, coupons, etc. Additional direct beneficiaries are throughout supply chain, pharmaceutical, logistics, law enforcement and payment industries.